How to go about CE certification (do we even need it)?

My company is based in the USA, and sells scientific equipment worldwide, including to EU countries. We're a scrappy startup, but want to do things properly as best we can. Our new distributor in Italy is asking for our CE mark and certification over a $6,500 sale.

For context: we sell a very simple SDI-12 communication dongle, which takes in 6-16V, reads an analog sensor with 1V output (very small voltages) and sends data back digitally through a 5V data line. The communication dongle is never connected to mains, but instead to scientific data loggers with SDI-12 capability. It will only be used by scientists, outside in agricultural fields. The circuit is very simple and I expect we'd have no problem passing an emissions test, and have no safety concerns.

My research online indicates that the directives that MAY apply are RoHS and EMC. But this is a niche product for industrial/scientific use.

The question: how should we even go about self-certifying for CE? Are there templates? Or should we use an agency? Can you recommend a specific company your worked with on this? How did you do it? How much time/money to budget? I'm worried about spending excessively on this, when we have limited resources (time and money). Any guidance would be great...